An earset is an audio equipment that is disposed in an earflap or auricle and an external auditory meatus to listen to a sound, for example, an in-ear earphone.
If the earset is disposed in the external auditory meatus, there is a pressure difference between an inner side (human pressure) and an outer side (atmospheric pressure) of the earset. In other words, when an ear cap or tip of the earset is brought into close contact with an inner wall of the external auditory meatus, a pressure difference occurs between the inner and outer sides of the earset.
A vibrating diaphragm is influenced by the pressure difference, and thus may be offset toward the outer side of the earset.
In order to prevent the vibrating diaphragm from being offset, a dynamic driver unit and a balanced armature driver unit are provided at their backs with a back hole. The back hole is to equally maintain the atmospheric pressure between the inner and outer sides of the earset. This causes the vibrating diaphragm to vibrate at a proper position. In addition, in case of covering the back hole with dampers having different mesh density or the like, a pressure difference occurs between the dampers upon operation of the vibrating diaphragm, which is used for tuning.
There is a problem in that the back hole serves as a passage through which an extraneous noise passes. In order to use the earset at a place where is required to completely cancel the extraneous noise, for example, an airport or the like, the extraneous noise should be completely cancelled. However, it is hard to completely cancel the extraneous noise due to the back hole formed in the back of the driver unit.
Meanwhile, the earset integrated with a speaker and a microphone carries out in one body a function of transmitting a sound to an external auditory meatus and a function of collecting a sound of a user. In general, the speaker is disposed toward the external auditory meatus to transmit the sound, while the microphone is exposed outwardly from the auricle to collect the sound of the user. Even in case of such an earset, there is a problem in that an extraneous noise is input through a sound collecting hole which is formed in the microphone to collect the sound, and then the extraneous noise comes in through the back hole formed in the back of the driver unit. In case of an in-ear microphone with a microphone facing the external auditory meatus, there is a problem in that a sound quality is deteriorated due to the extraneous noise, regardless of an installation position of the in-ear microphone. To prevent the above problem, if the back hole formed in the back of the driver unit is closed, the vibrating diaphragm is offset, so that the in-ear microphone cannot be used in an aircraft or a mountainous area.
Therefore, it is necessary to cancel the extraneous noise outputting from the back holes formed in the backs of the dynamic driver unit and the balanced armature driver unit and allow air to flow.